1. Field of the Invention
The present invention relates to an electron emitting apparatus for emitting field electrons from a cathode thereof, a manufacturing method therefor and a method of operating the electron emitting apparatus. More particularly, the present invention relates to a flat electron emitting apparatus having a cathode formed into a flat shape, a manufacturing method therefor and a method of operating the flat electron emitting apparatus.
2. Related Background Art
In recent years, display units have been researched and developed such that the thickness of the display unit is attempted to be reduced. In the foregoing circumstance, a field emission display (hereinafter abbreviated to xe2x80x9cFEDxe2x80x9d) incorporating so-called electron emitting apparatuses has attracted attention.
As shown in FIG. 1, the FED has portions each of which corresponds to one pixel, the portion including a spint electron emitting apparatus 100 and a fluorescent surface 101 formed opposite to the spint electron emitting apparatus 100. A multiplicity of the foregoing pixels are formed into a matrix configuration so that a display unit is constituted.
In the portion corresponding to one pixel, the electron emitting apparatus 100 incorporates a cathode 103 formed on a cathode panel 102; a gate electrode 105 laminated on the cathode 103 through an insulating layer 104; and electron emitting portions 107 each of which is formed in each of a plurality of openings 106 formed in the gate electrode 105 and the insulating layer 104. The FED has the fluorescent surface 101 formed opposite to the electron emitting apparatus 100. The fluorescent surface 101 is composed of a front panel 108, an anode 109 and a fluorescent member 110 formed on the front panel 108. Moreover, the FED is structured such that predetermined voltages are applied to each of the cathode 103, the gate electrode 105 and the anode 109, respectively.
Each of the electron emitting portions 107 of the FED is formed into a cone-like shape realized by finely machining a material, such as W, Mo or Ni. The leading end of the electron emitting portion 107 is disposed apart from the gate electrode 105 for a predetermined distance. The electron emitting apparatus 100 is structured such that electrons are emitted from the leading ends of the electron emitting portions 107. The electron emitting apparatus 10 has a multiplicity of the electron emitting portions 107.
In the FED structured as described above, a predetermined electric field is generated between the cathode 103 and the gate electrode 105. As a result, electrons are emitted from the leading ends of the electron emitting portions 107. Emitted electrons collide with the fluorescent member 110 formed on the anode 109. As a result, the fluorescent member 110 is excited to emit light. When the quantity of electrons which are emitted from the electron emitting portions 107 of the FED corresponding to the pixels is adjusted, a required image can be displayed on the display unit.
When the spint electron emitting apparatus is manufactured, the openings 106 are formed such that the diameter of each opening 106 is about 1 mm. Then, the electron emitting portions are perpendicularly evaporated in the surfaces of the openings 106. Specifically, a separation layer is formed on the gate electrode 105 after the openings 106 have been formed. Then, a metal film or the like is formed. As a result, the metal film is formed on the gate electrode 105 and the bottom surfaces of the openings 106. Then, the film forming operation is continued to grow the metal film so that the cone-line electron emitting portions 107 are formed. Then, the metal film formed on the gate electrode 105 is, together with the separation layer, removed.
However, the cone-like electron emitting portions of the spint type electron emitting apparatus cannot easily be formed. Thus, there arises a problem in that a stable electron emitting characteristic cannot be realized. The reason for this lies in that the electron emitting characteristic of the spint electron emitting apparatus considerably depends on the distance between the leading end of each of the electron emitting portions and the gate electrode. Therefore, the electron emitting portions cannot reliably be formed.
When the electron emitting portions are formed, the process for forming the metal film on the gate electrode having a large area and removal of the metal film and the separation layer from the same must uniformly be performed. If the metal film cannot uniformly be formed or if the metal film and the separation layer cannot uniformly be removed, electrons cannot easily be generated from the electron emitting portions by dint of the electric field generated from the gate electrode.
When electron emitting portions are formed to correspond to a large screen, satisfactory perpendicularity cannot be realized in a film forming direction over the screen. Therefore, uniform electron emitting portions cannot easily be formed on the overall surface of the screen. What is worse, contamination sometimes occur when the metal film and the separation film are removed. Thus, there arises a problem in that satisfactory manufacturing yield cannot be obtained.
To overcome the problems experienced with the spint electron emitting apparatus, a flat electron emitting apparatus has been suggested which has a structure that a high electric field is applied to the edge of a metal electrode so as to emit field electrons.
The flat electron emitting apparatus has a structure that an emitter electrode formed into a plate-like shape is held between a pair of gate electrodes through insulating layers. Thus, an electric field generated between a pair of gate electrodes and an emitter electrode causes electrons to be emitted from the emitter electrode.
The structure of the flat electron emitting apparatus permits the emitter electrode for emitting electrons to be formed into the plate-like shape. Therefore, the flat electron emitting apparatus can easily be manufactured as compared with the above-mentioned spint electron emitting apparatus.
Also the flat electron emitting apparatus must enlarge the electric field which is generated between the emitter electrode and the pair of the gate electrodes in order to improve the electron emitting characteristic. To enlarge the electric field, the emitter electrode must furthermore be fined so as to furthermore reduce the curvature radius of the leading end of the emitter electrode.
However, if the emitter electrode of the flat electron emitting apparatus is simply fined, the mechanical strength of the emitter electrode decreases considerably. Therefore, a great electric field cannot be generated. If a great electric field is applied to the fined emitter electrode, the emitter electrode is sometimes broken. Thus, the foregoing fine emitter electrode cannot be used in a high electric field.
Hitherto, the curvature radius of the leading end of the emitter electrode can be reduced during a process for manufacturing the flat electron emitting apparatus only when exposing, developing and etching conditions for the photoresist are delicately controlled. Therefore, the conventional method cannot easily form an emitter electrode of the type having satisfactory mechanical strength and provided with the leading end having a small curvature radius.
What is worse, the flat electron emitting apparatus suffers from a poor quantity of electrons which reach the anode as compared with the spint electron emitting apparatus. Therefore, the flat electron emitting apparatus cannot cause the fluorescent member disposed on the anode to satisfactorily emit light.
Accordingly an object of the present invention is to provide an electron emitting apparatus and a manufacturing method therefor which is capable of overcoming the problems experienced with the conventional electron emitting apparatus, which exhibits satisfactory mechanical strength and which is able to satisfactorily emit electrons.
Another object of the present invention is to provide a method of operating the electron emitting apparatus such that electrons generated by the electron emitting apparatus can efficiently reach the anode.
To achieve the above-mentioned object, according to an aspect of the present invention, there is provided an electron emitting apparatus comprising: a first gate electrode formed on a substrate; a cathode formed on the first gate electrode through a first insulating layer and having a projection projecting over the first insulating layer; and a second gate electrode formed on the cathode through the second insulating layer, wherein the cathode has a structure that the projection is provided with an inclined surface having a thickness which is reduced toward the leading end of the projection.
The electron emitting apparatus according to the present invention is structured as described above so that an electric field is generated among the first gate electrode, the second gate electrode and the cathode. The electric field causes electrons to be emitted from the leading end of the cathode. The electron emitting apparatus according to the present invention has the inclined surface formed such that the thickness of the projection of the cathode is reduced toward the leading end of the projection. Thus, the curvature radius of the leading end of the cathode is reduced. That is, the portion of the cathode adjacent to the first and second insulating layers has a large thickness as compared with that of the leading end. Therefore, the electron emitting apparatus enables the leading end of the cathode to have an excellent field electron emitting characteristic. Moreover, the dynamic strength of the cathode adjacent to the first and second insulating layers can be increased.
To overcome the above-mentioned problem experienced with the conventional structure, according to another aspect of the present invention, there is provided a method of manufacturing an electron emitting apparatus comprising the steps of: forming, on a substrate, a first gate electrode layer, a first insulating film, a cathode layer, a second insulating film and a second gate electrode layer in this sequential order; forming a first opening in a predetermined region of the second gate electrode layer and causing the second insulating film to be exposed through the first opening; isotropically etching the second insulating film exposed through the first opening to expose the cathode layer through an opening having a size larger than the size of the first opening; anisotropically etching the cathode layer to form a second opening and causing the first insulating film to be exposed through the second opening; and isotropically etching the first insulating layer exposed through the second opening to cause the first gate electrode layer to be exposed, wherein the step for forming the second opening is performed such that the cathode layer is anisotropically etched so that an inclined surface having a thickness which is reduced to an end of the opening is formed.
The method of manufacturing the electron emitting apparatus structured as described above is performed such that the cathode layer is exposed such that the size of the opening is made to be larger than the size of the first opening. In this state, anisotropic etching is performed so that the second opening is formed. That is, the foregoing method is performed such that the region of the exposed cathode adjacent to the second insulating layer is covered with the second insulating film and the first gate electrode layer from an upper position. Therefore, anisotropic etching for forming the second opening is performed such that the rate at which the exposed cathode is etched is reduced in a direction toward the second insulating layer. Therefore, the foregoing method is able to easily form the second opening having the inclined surface, the thickness of which is reduced toward the end of the second opening.
To achieve the above-mentioned object, according to another aspect of the present invention, there is provided a method of manufacturing an electron emitting apparatus comprising the steps of: forming, on a substrate, a first gate electrode layer, a first insulating film, a cathode layer, a second insulating film and a second gate electrode layer in this sequential order; forming a resist film having an opening corresponding to a predetermined region of the second gate electrode layer; anisotropically etching the resist film and the second gate electrode layer exposed through the opening to form a first opening so as to cause the second insulating film to be exposed through the first opening; isotropically etching the second insulating film exposed through the first opening to expose the cathode layer through an opening having a size which is larger than the size of the first opening; anisotropically etching the exposed cathode layer to form a second opening and causing the first insulating film to be exposed through the second opening; and isotropically etching the first insulating layer exposed through the second opening so as to expose the first gate electrode layer, wherein the step for forming the first opening is performed such that an inclined surface having a thickness which is reduced toward an end of the first opening is formed, and the step for forming the second opening is performed such that the cathode layer is anisotropically etched together with an end of the first opening so that the inclined surface provided for the first opening is transferred so that an inclined surface having a thickness which is reduced toward an end of the first opening is formed.
The method of manufacturing an electron emitting apparatus according to the present invention is structured as described above such that the first opening having the inclined surface, the thickness of which is reduced toward the end of the first opening, is formed. Then, the cathode layer is anisotropically etched together with the inclined surface of the first opening in a state in which the cathode layer is exposed in such a manner that the size of the opening is larger than the size of the first opening. Thus, the second opening is formed. Therefore, the foregoing method is performed such that the anisotropic etching operation for the purpose of forming the second opening results in the etching rate of a region of the exposed cathode layer adjacent to the second insulating layer being reduced owing to an influence of the inclined surface provided for the first opening. As a result, the second opening having the inclined surface having the thickness which is reduced toward the end of the second opening can be formed by the above-mentioned method.
To achieve the above-mentioned object, according to another aspect of the present invention, there is provided a method of operating an electron emitting apparatus such that an electron emitting apparatus having a first gate electrode, a cathode formed on the first gate electrode through a first insulating layer and a second gate electrode formed on the cathode through a second insulating layer which are formed on a substrate is operated, the method of operating an electron emitting apparatus comprising the step of: applying voltages to satisfy a relationship as V2 greater than V1 greater than Vc on an assumption that voltage which is applied to the first gate electrode is V1, voltage which is applied to the cathode is Vc and voltage which is applied to the second gate electrode is V2.
The method of operating the electron emitting apparatus according to the present invention and structured as described above is performed such that the voltage which is positive with respect to the cathode is applied to the first and second gate electrodes. Therefore, an electric field is generated among the first gate electrode, the second gate electrode and the cathode. Since the electric field is applied to the cathode, the cathode emits electrons. At this time, a voltage higher than the voltage which is applied between the first gate electrode and the cathode is applied between the second gate electrode and the cathode. Therefore, the electric field which is generated from the first gate electrode and the second gate electrode causes electrons emitted from the cathode to move to the second gate electrode. Therefore, the above-mentioned method enables electron generated by the cathode to be extracted in a direction of the second gate electrode.